Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $58.93   13.302%   $66.7689   $66.77   $66.75   $66.80  
  Purchase #2 $159.93   7.104%   $171.2914   $171.29   $171.30   $171.30  
  Purchase #3 $162.60   9.602%   $178.2129   $178.21   $178.20   $178.20  
  Purchase #4 $57.31   11.164%   $63.7081   $63.71   $63.70   $63.70  
  Purchase #5 $81.98   8.804%   $89.1975   $89.20   $89.20   $89.20  
  Purchase #6 $219.62   13.165%   $248.533   $248.53   $248.55   $248.50  
  Purchase #7 $196.47   9.294%   $214.7299   $214.73   $214.75   $214.70  
  7 purchase totals = $936.84       $1,032.4417   $1,032.44   $1,032.45   $1,032.40